The invention relates to a device for delivering dry medication particles from an MDI (metered dose inhaler) or dry powder medication measuring device to an intubated patient through a ventilator circuit or an anesthesia device, and more particularly to a device which reduces or minimizes absorption of humidity by minute, dry, light medication particles and thereby prevents them from gaining weight and falling out of the inspiratory airstream before they reach their targeted sites.
In prior devices for the administration of aerosol medication to intubated patients, the aerosol is delivered directly into tubing of a ventilator and carried with air or oxygen into the patient's lungs. FIG. 1 shows a typical ventilator circuit, including a ventilator 1 having an expiratory tube 33 by means of which air is expelled as indicated by arrow 1A from the lungs of a patient through an endotracheal tube 7 into a Y connector 3, an expiratory tube 33 and into ventilator 1. Ventilator 1 also forces a measured regulated inspiratory stream 1B of air or oxygen through an inspiratory tube 32, a valved T connector 5 of the type disclosed in U.S. Pat. No. 4,951,661, Y connector 3, and endotracheal tube 7 into the lungs of the patient, to thereby provide ventilation, i.e., assisted breathing. In some cases, a heated wire (not shown) extends through inspiratory tube 32 to heat the inspiratory stream 1B, which usually is humidified, to thereby prevent cooling of the inspiratory stream and resulting condensation of moisture from it onto the walls of the inspiratory path. (Typically, ventilator 1 includes a humidifying device for inspiratory stream 1B, since ordinarily it is harmful to provide dry air or oxygen to the lungs of a patient.)
Commonly, a passive humidifier 6 such as a "heat and moisture exchanger" (HME) or "hygroscopic condenser humidifier" (HCH) air filtering and humidifying device is coupled between one port of the Y connector 3 and the proximal end of endotracheal tube 7. Frequently, an adapter 4 is coupled in line with inspiratory tube 32 to allow aerosol medication from an MDI canister 14 to be introduced into the inspiratory air or oxygen stream 1B. The adapter 4 includes a nozzle that ejects an expanding aerosol plume when the MDI canister 14 is actuated. The aerosol plume produced by MDI aerosol canister 14 includes very finely divided medication particles, typically in the 1-10 micron diameter range. Inside the MDI canister 14, such medication particles are suspended in a pressurized liquid propellent. Upon actuation, a metered dose of the suspension is injected through the outlet stem of the canister through the nozzle of the adapter 4 to form the expanding plume. The drug-bearing liquid propellent breaks up into small droplets, which must evaporate to release the dry 1-10 micron medication particles. As the aerosol plume from MDI canister 14 is ejected into the inspiratory stream 1B, the released, dry, very light medication particles are carried in the humid air or oxygen inspiratory stream 1B for the brief time required to reach the intended therapeutic sites inside the patient's lungs. Drying of medication particles carried by the liquid propellant may be impeded by humidity in the inspiratory airstream.
The released medication particles are light enough to be efficiently carried by the inspiratory air stream 1B through the curved path defined by the inspiratory apparatus into the patient's lungs. The medication particles may be hygroscopic, and hence may absorb water molecules and grow in size and weight as they travel through the moisture-laden inspiratory airstream 1B. In that case, droplets formed around the medication particles become relatively heavy, and many of them therefore have a tendency to "fall out" of the inspiratory stream 1B by impinging on and coalescing on the walls of the tubing and bronchi, and therefore not reach the therapeutic sites in the patient's lungs.
When dry powder drug dispensing devices are used, the humidity of the inspiratory air stream 1B is not conducive to efficient dispersion and effective delivery of the dry powder to the therapeutic sites in the patient's lungs, especially if the powder is hygroscopic and results in condensation of droplets on the medication particles, which gain weight and then impinge on the walls of the tubing or upper bronchi and are lost from the quantity of medication intended to be carried to the lungs of the patient. Therefore, the effective medication dose is reduced for either MDI medication or dry powder medication.
Another problem of the prior art arises in ventilation circuits which include a "heat and moisture exchanger" (HME) or a "hygroscopic condenser humidifier" (HCH) 6 connected with the Y connector, plus an aerosol medication delivery device in the inspiratory path 1B. This arrangement necessitates removing the HME or HCH 6 from the ventilator circuit to allow the individual medication particles carried by inspiratory stream 1B to reach the proximal end of the endotracheal tube 7. This interruption of the inspiratory stream 1B is undesirable, as it may expose the patient or caregiver and the interior of the tubing and ventilator to airborne bacteria and/or viruses.
In another arrangement of prior art, introducing the aerosol or dispersed dry drug material downstream from the HME or HCH can result in undesirable increasing of the "dead-volume" air, i.e., air which is rebreathed by the patient.
Yet another problem of the prior art devices is that none of them allow an MDI drug to be introduced into the ventilator circuit by means of the nozzle of the same inhaler or delivery system which is provided with the MDI canister by the drug supplier. Consequently, the MDI canister 14 must be removed from the manufacturer's inhaler nozzle and separately inserted into the nozzle of the ventilator adapter 4.
There clearly is an unmet need for a method of providing delivery of MDI medication into a ventilator circuit using the same nozzle supplied by the manufacturer.